I wonder if anyone can clear up some concerns I have with my 4L60E TCC lockup?


What actually dictates when it will and wont lock up?


I understand that the TPS and brake switches play a key role here, but with the way mine is working it leads me to believe there's more to it?


For example, I can get my car out and go for a steady drive and once the engine is warmed up the TCC will engage (and I will feel it engage positively) as soon as im into 4th and above about 43 mph.


If I then go onto the motorway/highway and floor the throttle on the slip road to get up to say 80 mph, once ive slowed back down to 60 or 70 the TCC wont engage - or at least it doesn't feel like it has. The revs will sit at 2000rpm at 70 as it does with TCC engaged, but if I blip the throttle just a small amount I can see the rpms increase with slip. The TCC never seems to engage for the rest of the journey and ill have to turn the car off and let is stand before starting up again and seeing the TCC working as I expect.


Now if on another drive I don't floor the throttle going up the slip road, ill feel that positive engagement of the TCC and if I blip the throttle I don't see the rpms increase - its fully locked in.


Why would this be happening?


Thanks

 

The only way to know for sure is to hook up a scan tool and log what exactly is going on. Then, going on from there, you can proceed to mechanical or electronic problems and solutions.

 

Thanks for getting back to me.

Yes I'm going to have to bite the bullet and buy HP tuners.

This strange TCC behaviour only started after I replaced the TPS (ended up going through 3 TPS before getting a good one)

The TPS was set at 0.53 volts at idle and a relearn carried out. My original TPS was set to 0.058 volts at idle as nobody had set it up properly...I had harsh shifts into drive and reverse, but the TCC worked all the time. When I reset the original TPS to 0.5 volts at idle I discovered a dead spot just after 1 volt which would make the car jerk under throttle. So I replaced that with an AC Delco professional one which then proceeded to fall to pieces. My third TPS was a standard motor products one which has been on for about 6 months and whilst the harsh shifts and other driving issues have gone it's now the TCC that behaves odd.

 

As RevGTO says, the PCM completely controls the TCC lockup and sometimes it has a strange mind of its own. As you learned, the PCM can be very sensitive to engine sensors.
Of course if the PCM commands lockup and it doesn't happen, it is a trans or converter issue; some are quite easy to fix.

 

I did 450 miles over the last two days. Most of this was highway driving. I can honestly say I think this problem must be in my head rather than a genuine problem.

I think part of the issue for me is that I remember how the TCC behaved before I changed the TPS. As my line pressure was at maximum all of the time, the TCC engaged as if it was another gear shift. Now it is much softer but I have established that the TCC is working. Observing its operation over the last few days and that 450 miles , I can see that depending on my speed, throttle position and how hard I've been driving that it alters how the TCC engages but ultimately it does lock in and stay firmly locked as it should.


I guess this will be down to the PWM duty cycle doing what it should. After a WOT blast, once I've settled down to 70 mph, after about 20-30 seconds the revs gently drop and the TCC is locked. If I'm cruising around and below 50% throttle, once I get above 45mph the TCC locks quite firmly with a slight press of the throttle and then stays locked as it should until I brake or drop below 43mph. If I brake but then get back on the throttle it again firmly locks. I guess it was the "gentle" transition into lock up at higher speeds that was making me think it wasn't working.

 

Factory lock up/disengage is soft. PWM
With my compushift and the converter with the triple clutch feels like your getting bumped from the rear when it locks up.